There are many methods for reducing bezel width in the prior art. Direct view backlights, where LEDs are distributed behind an LCD and shine directly through, in principle have a very low bezel width but in general are too thick and expensive for a small area application. Such small area applications (of display sizes approximately 15 inches in diagonal or less) typically use lightguides with patterned extraction features and edge emitting LEDs to illuminate the LCD. This enables less LEDs to be required and very thin form factors. However the area around the LED must be obscured as the high brightness and non-uniformity of this area would mean a display could not be positioned over this area. The area around the LED incorporates the flat panel connector electronics, the LED itself and the mixing area of the lightguide, where it is not possible to achieve uniformity by extraction feature control alone. This obscuration would be the limiting bezel width, meaning that a black area of at least 2-3 mm exists at the LED end of the lightguide.
Reducing this bezel area to create more usable display area for the device size has been a source of study. A cross section of the types of prior art are summarized below:
JP 4552095 (Stanley Electric) positions the LEDs at the corner of the lightguide where the natural spread of the LED light better fills the lightguide area.
U.S. Pat. No. 8,451,398 (Panasonic), U.S. Pat. No. 8,755,007 (Seiko Epson) and JP2010056089 (Sharp) describe reflecting structures on the far side of the lightguide that efficiently reflect light back in order to improve uniformity near the LEDs.
U.S. Pat. No. 8,911,133 (Opto Design) utilizes an air-guide with LEDs illuminating an airgap between highly reflecting areas and an array of apertures are used to achieve uniformity. This system is relatively thick and proposed mainly for lighting applications.
US 20090015753 (Wintek) and U.S. Pat. No. 6,935,764 (Samsung) describe structures on the area near the LEDs molded into the lightguide in order to better spread the light to reduce the mixing area.
US20050180165 (Seiko Instruments) describe a secondary lightguide member that makes the LED illumination more uniform into the main lightguide.
The above-referenced documents only reduce the mixing width in the lightguide, though they do not attempt to reduce the bezel width to less than that of the LEDs themselves.
A number of prior-art references such as US20110090423 (3M) and JP2010040246 (Seiko Epson) attempt to thin the structure by adding lightguide elements to an LED array as used in a direct view backlight. This is to reduce the thickness of a direct view system in order to achieve a thinner unit.
Attempts to hide the LEDs on an edge based system include U.S. Pat. No. 6,951,401 (Philips) and US20060255346 (Minebea) where the LEDs and lightguide are wrapped around beneath the main lightguide and secondary lightguides are used underneath the main lightguide.
Prior art such as CN202210196 (Shenzen Huaxing) and JP2006244825 (Sharp) use patterned filters above the LEDs in order to reduce the non-uniformity.